By Mitchell Stocki
In October 2011, Native Lands Environmental & Prince Contracting faced the difficult challenge of dewatering an entire lake in order to build a new bypass road extension in Sarasota, FL. The new Exit 213 required the complete dewatering of one lake while discharging the water into an adjacent waterbody recognized as a world class rowing lake in pristine condition.
Approximately 25 million gallons of water had to be removed for construction. To complicate matters, road construction operations had disturbed 90% of the soil around the soon-to-be-dewatered lake, making any significant rain event more challenging by adding to the already high levels of turbidity. Sediment control was a major concern.
Project engineers sought to find a reliable and cost-effective solution that would reduce turbidity and eliminate any chance of bio-accumulation that could potentially be toxic to the lake fish. After meeting with engineers and inspectors from Southwest Florida Stormwater management, as well as with Prince Contracting and Wilbur Smith & Associates, it was concluded that the HaloKlear dual biopolymer system could address the challenges.
The dual biopolymer system uses chitosan-based flocculent to trap hydrocarbons, metals and nutrients. It works on virtually any soil type and a wide range of pH levels, and the natural biopolymers are 100% biodegradable.
Getting Started
At the project site, initial influent Nephelometric Turbidity Units (NTUs) measured between 172 and 846. Per Florida regulations, effluent levels may not exceed 29 NTUs over background. At this site, background was 3 NTUs; therefore, discharge could not exceed 32 NTUs.
Tests were conducted to determine the appropriate dose of polymer. Because of the changing conditions of the soil to the dewatering area, the system's onsite jar test kits and calculator provided an extra value to the contractor by providing an immediate dose response. This made it possible to quickly make adjustments to optimize dose and eliminated the expense and hassle of sending samples off to outside labs.
Once the tests were completed, a simple manifold kit was built to house the dual biopolymer socks. (see Fig. 1). Turbid water is directed through the system under gravitational flow to a sediment basin system, in this case, sediment bags.